Methodological progress note: Hybrid effectiveness‐implementation clinical trials

School of Nursing, Midwifery and Social Work, The University of Queensland, Brisbane, Queensland, Australia Centre for Children's Health Research, Children's Health Queensland Hospital and Health Service, Brisbane, Queensland, Australia NHMRC Centre for Wiser Wound Care, Griffith University, Brisbane, Queensland, Australia Centre for Clinical Nursing, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA Penn Implementation Science Center at the Leonard Davis Institute (PISCE@LDI), University of Pennsylvania, Philadelphia, Pennsylvania, USA Penn Medicine Nudge Unit, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA Section of Hospital Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA


INTRODUCTION
Randomized controlled trials (RCTs) remain the gold-standard approach to informing clinical decision-making and drawing causal inferences. 1,2 Yet, traditional RCTs have limitations. [1][2][3][4] Conducting these trials can be painstakingly slow and translation to practice even slower, resulting in meaningful and unacceptable research-topractice gaps. There is often a disconnect in generalizability and performance between the highly controlled clinical trials to the real-world application of approaches within complex health environments across situational contexts. Implementation science has emerged as a distinct area of research specifically to bridge the clinical evidence to practice gap.
It is the formal study of methods to promote the systematic uptake of research findings and other evidence-based practices (EBPs) into routine practice, and, hence, improve the quality and effectiveness of health services. 5 The inclusion of EBPs in the definition means that implementation science as originally conceived was intended to promote interventions that were already proven to be effective. In implementation trials, implementation strategies (such as educational outreach, coaching, facilitation, audit and feedback, and clinical decision support) are tested to determine the best way to promote EBP use.
To reduce the gap in translating effective knowledge from clinical trials, separate effectiveness and implementation trials need not be performed in series, but rather learnings can occur together. 3 Healthcare systems are complex and understanding the influence of situational context in parallel to understanding the clinical effectiveness is vital, even while the evidence base is actively being developed in clinical trials (individually or clusterrandomized) or in quasi-experimental studies. We argue that the most important test of an intervention is its test within the context in which it is meant to be deployed. The hybrid effectiveness-implementation design offers an innovative and rapid manner to test effectiveness and implementation at the same time.
This methodological progress note has been developed to prepare the Hospital Medicine community to appropriately use hybrid effectiveness-implementation trials in our own research and ensure, as hybrid trials become more common, we are informed in design attributes, strengths and limitations as educated consumers of health and healthcare delivery literature.

HYBRID EFFECTIVENESS-IMPLEMENTATION CLINICAL TRIALS
A hybrid trial has two complementary goals, incorporating an exploration of both clinical effectiveness (i.e., does this intervention improve this clinical outcome) and implementation outcomes (i.e., how is this intervention applied) within a single trial. Hybrid trials are serious undertakings and require advanced expertise in multiple quantitative and qualitative methods. There is a range of implementation frameworks that exist to guide the design of a robust hybrid trial, including process frameworks, determinant frameworks, and evaluation frameworks. 6 Below we have listed a few of the most frequently used outcomes within implementation frameworks, with definitions adapted from a landmark paper by Proctor et al., 7 and COVID-specific updates by Pilar et al., 8 and encourage the readership to continue their learning via these papers. Please note that below, each outcome is framed relative to an EBP, but could also be framed relative to an implementation strategy (e.g., acceptability of a strategy).
• Acceptability is the degree to which those who might be involved or affected by implementation welcome implementation of a new EBP and/or view it as appealing and meeting their approval. It is often measured by survey (e.g., Acceptability of Intervention Measure). 9 • Adoption is the initial decision or action to begin using a new EBP.
This outcome can be measured via survey or by analyzing existing administrative or clinical data to determine uptake of the EBP.
• Fidelity is the degree to which an EBP is implemented as designed or intended, and may include dimensions of adherence to the original plan, the "dose" of intervention delivered, and the quality of intervention delivery. Fidelity can be measured via checklists, self-report, and direct observation of the practice.
• Health equity involves fair access to treatment or innovation without avoidable or remediable differences among groups of people. 8 • Penetration (also known as reach) is the degree to which an EBP is integrated into the desired setting and subunits of that setting (e.g., the percentage of wards in a hospital using an EBP, or the percentage of eligible patients who receive an EBP within a primary care system).
• Sustainability is the extent to which an EBP is continued over an extended period of time beyond an initial period of adoption.
Associated measures that might promote the sustainment of an EBP are institutionalization and routinization.
In addition to exploring how EBPs can be successfully implemented, hybrid trials can by their design provide insight into the effectiveness of the studied intervention, especially if the clinical outcome was unexpected. Why wasn't the expected benefit seen?
What contributed to the difference between expected and obtained results? Hybrid trials can answer broader questions than those related to effectiveness alone. For example, the information was disseminated but not widely accepted or adopted. Or, the intervention was delivered with low fidelity and/or dose. Hybrid trials multiply the amount of learning that can come from a trial without always dramatically multiplying the cost. They can answer implementation science-based questions that are broader than the clinical disease and are broadly relevant to implementation in hospitals, clinics, and wider services.

TYPES OF HYBRID TRIALS
Hybrid trials exist on a continuum, with the three designs varying based on their primary focus and the amount of emphasis on effectiveness versus implementation outcomes (see Table 1 and Figure 1

THE FUTURE
In the future, all "good" trials will be hybrid, in some way. Delays in the traditional research pipeline cause patients to receive suboptimal care, which is unacceptable and fixable. However, resources need to be developed to ensure hybrid trials are achievable and rigorous in their execution. Dedicated funding streams are necessary to both fund high-quality hybrid trials and advance their methodological science. We hope that this methodological progress note increases awareness of the opportunities that this trial design presents and galvanizes those doing effectiveness trials to consider incorporating these approaches into their own work.